The direct synthesis of amides and nitriles from readily available aldehyde precursors provides access to functional groups of major synthetic utility. To date, most reliable catalytic methods have typically been optimized to supply one product exclusively. Herein, we describe an approach centered on an operationally simple iron-based system that, depending on the reaction conditions, selectively addresses either the CO or C–H bond of aldehydes. This way, two divergent reaction pathways can be opened to furnish both products in high yields and selectivities under mild reaction conditions. The catalyst system takes advantage of iron’s dual reactivity capable of acting as (1) a Lewis acid and (2) a nitrene transfer platform to govern the aldehyde building block. The present transformation offers a rare control over the selectivity on the basis of the iron system’s ionic nature. This approach expands the repertoire of protocols for amide and nitrile synthesis and shows that fine adjustments of the catalyst system’s molecular environment can supply control over bond activation processes, thus providing easy access to various products from primary building blocks.
An adaptive catalytic system that provides control over the nitroarene hydrogenation network to prepare a wide range of aniline and hydroxylamine derivatives is presented. This system takes advantage of a delicate interplay between a rhodium(III) center and a Lewis acidic borane introduced in the secondary coordination sphere of the metal. The high chemoselectivity of the catalyst in the presence of various potentially vulnerable functional groups and its readiness to be deployed at a preparative scale illustrate its practicality. Mechanistic studies and density functional theory (DFT) methods were used to shed light on the mode of functioning of the catalyst and elucidate the origin of adaptivity. The competition for interaction with boron between a solvent molecule and a substrate was found crucial for adaptivity. When operating in THF, the reduction network stops at the hydroxylamine platform, whereas the reaction can be directed to the aniline platform in toluene.
Es wird ein adaptives katalytisches System vorgestellt, das die Kontrolle über das Nitroaren-Hydrierungsnetzwerk zur Herstellung einer breiten Palette von Anilin-und Hydroxylaminderivaten ermöglicht. Dieses System profitiert von einem delikaten Zusammenspiel zwischen einem Rhodium(III)-Zentrum und einem Lewis-sauren Boran, das in die sekundäre Koordinationssphäre des Metalls eingeführt wird. Die hohe Chemoselektivität des Katalysators in Anwesenheit verschiedener potenziell angreifbarer funktioneller Gruppen und seine Bereitschaft, im präparativen Maßstab eingesetzt zu werden, veranschaulichen seine Praxistauglichkeit. Mechanistische Studien und Methoden der Dichtefunktionaltheorie (DFT) wurden eingesetzt, um die Funktionsweise des Katalysators zu untersuchen und den Ursprung der Adaptivität zu klären. Die Konkurrenz zwischen einem Lösungsmittelmolekül und einem Substrat um die Wechselwirkung mit Bor erwies sich als entscheidend für die Adaptivität. Bei der Reaktion in THF stoppt das Reduktionsnetzwerk an der Hydroxylamin-Plattform, während die Reaktion in Toluol auf die Anilin-Plattform gelenkt werden kann.
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